The present invention relates to pneumatic nail guns, and particularly to a pneumatic nail gun having a main passage and a bottom valve disposed at a peripheral portion of a fixed cylinder of the nail gun, for continuously guiding compressed high pressure air to drive a hitting piston of the nail gun upwardly reposit.
The pneumatic nail gun generally utilizes a compressed high pressure air to drive nails to punch, which is a gun-shaped pneumatic tool, and has been widely used in nailing woodworkers.
A typical pneumatic nail gun has a gun body, and a fixed or a moveable cylinder disposed in the gun body, which is used to control the compressed high pressure air to drive a piston in the cylinder to downwardly hit nails as well as upwardly reposit.
The related arts, such as U.S. Pat. No. 6,533,156, U.S. Pat. No. 6,779,699 and U.S. Pat. No. 6,006,975 respectively disclosed a typical pneumatic nail gun employing a fixed cylinder. The pneumatic nail gun includes a head valve disposed upon the fixed cylinder, and a trigger of the nail gun may drive the high pressure air to open the head valve so as to guide the high pressure air into the cylinder for driving the hitting piston downwardly move to hit nails. The nail gun also includes a return passage having a certain capacity disposed at a peripheral portion of the cylinder, and the return passage can guide high pressure air thereinto during the process of hitting nails by the hitting piston, and then the limited high pressure air in the return passage can drive the hitting piston upwardly move to reposit after hitting nails. However, the return passage can only collect compressed air during the hitting piston downwardly moving to hitting nails, which can not continuously guiding compressed air thereinto and maintaining a high pressure therein. Therefore, the pushing force generated by the limited compressed air in the return passage may not ensure the hitting piston having a stable reposition process. During the process of continuously hitting nails, slower and unstable reposition of the hitting piston may impact the speed and efficiency of hitting nails.
Other related arts, such as U.S. Pat. No. 4,784,308, U.S. Pat. No. 4,319,705 and U.S. Pat. No. 4,294,391 respectively disclosed a pneumatic nail gun overcome the above-mentioned problems. These nail guns includes a hitting piston induced by a valve, and a moveable cylinder. The residual compressed air in a bottom portion of the cylinder may be exhausted to atmosphere and high pressed air may be introduced into the bottom portion of the cylinder to driver the hitting piston upwardly move to reposit. On the other hand, these patents also disclosed valve mechanisms to substitute of return passages, for use in continuously guiding high pressure air into main air housing and a bottom chamber to drive the hitting piston upwardly move to reposit via opening passages of the main air housing and the bottom chamber when the trigger is released. However, the valve mechanisms are disposed in the gun body far away from the cylinder, it request that the gun body has a larger space and complicated passages to realize introducing the high pressure air into the bottom chamber to drive the hitting piston upwardly move to reposit. Therefore, the nail gun has a high manufacturing cost and complicated air flow passages.
Accordingly, what is needed is a pneumatic nail gun that can overcome the above-described deficiencies.